1. Field of the Invention
The invention relates to clutches and particularly to clutches which operate automatically by centrifugal force at a predetermined speed of rotation to disconnect a driving member from a driven member or load. More particularly, the invention relates to a centrifugal clutch construction in which the driving and driven members are uncoupled generally and instantaneously upon the members reaching a predetermined rotational speed without a reduction in coupling tension prior to the disengagement speed being reached, and with minimum clutch slippage.
2. Description of the Prior Art
There are numerous types and arrangements of centrifugal clutch constructions in which the drive and driven members are retained in coupled engagement until sufficient centrifugal force acts on certain clutch components to overcome the force of a retaining spring, whereupon the drive member disengages automatically from coupled engagement with the driven member. Many such clutch constructions experience excessive wear of the frictional coupling surfaces since the coupling disengagement is somewhat gradual as the coupled members come up to disengagement speed to overcome the srping tension. This results in undesirable slippage and heating between the coupling surfaces of the drive and driven members.
Some of these high speed release clutch constructions use spring biased levers and balls to retain the coupling surfaces in engaged position and to actuate the disengagement thereof upon reaching a predetermined rotational speed. Examples of such clutch constructions are shown in U.S. Pat. Nos. 2,432,591, 2,879,871, 2,879,872, 3,059,744, 3,319,755 and 3,747,731.
Various other clutch constructions use pairs of pivotally mounted toggle-like links to achieve disengagement at a predetermined speed. The links are adapted to move radially outwardly under the influence of centrifugal force and overcome a retaining spring or springs whereupon the applied pressure of the spring is removed from the coupled members to effect disengagement. Such action occurs upon the pivotally connected inner link ends moving sufficiently radially beyond a center line extending between the outer pivotally fixed ends of the links, such as shown in U.S. Pat. No. 1,316,466. A somewhat similar clutch construction uses pairs of links eccentrically attached to centrifugal balls as shown in U.S. Pat. No. 1,585,567.
These constructions use a pair of springs, one of which biases the midpoint of the link pairs toward their retracted coupling position, with the other spring biasing the drive coupling member into engagement with the driven coupling member. Such constructions, however, do not provide a rapid disengagement upon the coupled members reaching a predetermined speed which in certain clutch applications is desirable to reduce slippage and wear of the coupling surfaces. These prior art clutches have a linear clutch torque-speed characteristic since the retaining springs have a linear spring rate (force-displacement) characteristic; that is the disengagement force acting on the coupling spring and correspondingly on the coupling force between the driven and drive members is proportional to the centrifugal force acting on the links and centrifugal weights. These relationships provide a gradual disengagement between the coupled members as the clutch approaches disengagement speed causing such undesirable slippage and heating.
This linear relationship also increases the distances through which the retaining springs must move before clutch disengagement occurs. Therefore, the clutch may be larger than desired to accommodate this spring movement.
There is no known quick relase centrifugal clutch construction of which I am aware which provides an instantaneous disengageable clutch construction using a preloaded spring cartridge; providing a stepped distance-force relationship, requiring a relatively small motion to achieve a relatively large force amplification.